docs: def get_languages(self):
          """
          Return a list of all used languages for this page.
          """
          if self._languages:
              return self._languages
          self._languages = cache.get(self.PAGE_LANGUAGES_KEY % (self.pk))
          if self._languages is not None:
              return self._languages
  
          languages = [c['language'] for
              c in Content.objects.filter(page=self,
              type="slug").values('language')]
          # remove duplicates
          languages = sorted(set(languages))
          cache.set(self.PAGE_LANGUAGES_KEY % (self.pk), languages)
          self._languages = languages
          return languages